It's not a real extension sanctioned by the .TV registry unlike many other .co.xx domains. .co.tv is simply a .TV domain owned by one company and they are choosing to offer subdomains of it to the public. This seriously undermines its stability as there is nothing to stop the company from suddenly cancelling this offer at any time and all the sites you've built won't be accessible at that .co.cc URL anymore. I agree with the above poster Dreamerr and I wouldn't spend my time building a serious site on these domains unfortunately.
To be serious, I would too never waste time on building a site on 3rd party sub-domain. I would always go for my own domain.
it's nice sub domain but it's risky in the long run what if they just deiced to cancel this offer then your site will disappear , or maybe it's not free over all as they didn't provide much info on their site